1. Field of the Invention
This invention relates to a field emission device, and more particularly to a field emission device suitable for use for a field emission display (FED) or the like.
2. Discussion of the Background
An FED generally includes an envelope which is formed by sealedly joining a cathode substrate-side structure and an anode substrate-side structure to each other while being spaced from each other at a predetermined interval and is then evacuated to a high vacuum. The FED includes a field emission cathode (FEC), which may be constructed into a Spindt-type cold cathode structure. In the FEC of this type, application of a draw-out voltage to a gate electrode permits a conical emitter arranged in each of holes formed through the gate electrode to field-emit electrons, resulting in a phosphor of an anode electrode which has a positive voltage applied thereto emitting light, leading to display operation.
An FED of the high-voltage type exhibits increased luminance as compared with that of the low-voltage type, because in the former, a phosphor for a high voltage is increased in luminance. The FED of the high-voltage type is adapted to apply a voltage of several kV between an anode and a gate, so that it is needed to increase a gap between the anode and the gate. Thus, in the FED of the high-voltage type, it is required to focus electron beams emitted. In general, the FED has an FEC of the two-stage gate type incorporated therein. The FEC of the two-stage gate type is constructed so that a layer of a focusing electrode is provided separately from that of a gate electrode to provide a two-stage layer structure. This increases the number of layers, to thereby render manufacturing of the FEC costly and troublesome. In view of the problem, an FEC of the plane focusing type wherein a focusing electrode and a gate electrode are arranged in the same plane is proposed to simplify a process of manufacturing.
Such a plane focusing type FEC is generally constructed in such a manner as shown in FIGS. 5 and 6, wherein reference numeral 31 designates a focusing electrode, 32 is a gate electrode, 32a is holes, 11 is a conical emitter arranged in each of the holes 32a, 12 is an insulating layer, 13 is a cathode substrate, 33 is a resistive layer, and 34 is a cathode electrode line.
The plane focusing type FEC fails to fully surround the gate electrode 32 with the focusing electrode 31. Thus, the focusing electrode 31 and gate electrode 32, as shown in FIG. 5, each are formed into a pectinate configuration and arranged on the same plane on the insulating layer 12 while alternating with each other. The gate electrode 32 is formed at each of projections thereof with a plurality of holes 32a in a row in a longitudinal direction of the projection.
The cathode substrate 13, as shown in FIG. 6, is formed thereon with the cathode electrode line 34, on which the resistive layer 33 is arranged. Then, the insulating layer 12 is arranged on the resistive layer 33, followed by arrangement of the above-described focusing electrode 31 and gate electrode 32 on the insulating layer 12. The holes 32a are formed through the gate electrode 32 and insulating layer in a manner to commonly extend therethrough and the conical emitter 11 is arranged in each of the holes 32a while being placed on the resistive layer 33. The gate electrode 32 and focusing electrode 31 have a gate electrode voltage and a focusing electrode voltage applied thereto, respectively.
As described above, the plane focusing type FEC essentially fails to fully surround the gate electrode 32 with the focusing electrode 31. This causes electron beams emitted from the conical emitters 11 to leak through an opening of the focusing electrode 31 as indicated at an arrow in FIG. 5, resulting in failing to provide a desired spot diameter of electron beams.
Such a problem is due to the fact that the conventional plane focusing type FEC fails to arrange any electrode or structure between the gate electrode and a line for feeding a voltage to the gate electrode in a manner to surround the gate electrode. Thus, the problem is not restricted to only the focusing electrode. Also, the conventional plane focusing type FEC, even when the focusing electrode or structure is arranged so as not to fully surround the gate electrode, causes relationship in arrangement between the line for feeding a voltage to the gate electrode and the focusing electrode or structure to be subject to restriction.